Apparatus for impact pulverizing



l .l April 6, 1943. w M, SHEUDQN,vl A 2,316,124 APPARATUS Fon IMPACT PULVERIZING V Filed Aug. 1, 1940 M ATTO'RNEY .v :ward againstjthe. chamber wall. s

` not only loss of emciency lover what itwould be with true impact action onthe material, but also Patented Apr. 6, 1943 UNITED STATES PATENT, oFI-lca 'i I `APPARATUS FOR IMPACT PULVERIZING William M. Sheldon, Springfield N. 4J., assignorv I l to Louisltupr'echt, Montclair, N. J. i

1 lApplication August 1, 1940, Serial No. 349,097

- l sclalms. `(cia3-'11) Thislinventlon relates to the pulverization of o `material in impact pulverizers of the rotary beater, or hammer mill, type. The object of the invention is to" increase theemciencyfof such impact pulverizersand to avoid to a large degree loss of productioncapacity and ilneness of pulverization from wearon the striking faces of the beaters. 2

The pulverlzing action of impact pulverizers is generally considered to result. at least mostly,

' from, the impact between the rapidly rotating beatersand the material introduced into the mill chamber, andlargely `by the first impact of the,

lbeaters on the material as it is introduced through the feed `opening in the sldeof the peripheral wallof the chamber.` -The fact is, as.

l I have discovered.f`that the speed at whichthe material to `be pulverized is customarily `moved intothe mill chamberlis so low `as compared to ,the speed of rotation `oi' the beaters andthe resulting extremely small timefinterval between the passing of successive beaters pa'st the feed opening that the particlesof Vmaterial do not The invention such' materials soften when heated, and to avoid the softening of the material due to heat gener- 'ated by menen within me mln chamber, the o inert gas supplied to the injector is chilled. For

materials which soften when heated but arel not inflammable. chilled air may be used.

`enter completely between successive beatersbut U are merely struck by the outer edges of the beaters, which lthus tend `to shear off thin layers from the` particles throw the, particles out- This means,

that the 1 outer edges of the beaters become Iquickly dulled, thus greatly reducing the effi- 4"ciency of the mill; and the result isfnot only loss of production capacity, but also a general coarsening4 of the `pulverized product.

According to the present invention, the material t0 be pulverizedkls injected into the'mill chamber` and into, vand at approximately right angles to, the lpath of the beaters `in suspension in a stream of air-.or other suitable gas` drivem at auch highvelocity that by far thegreaterpart ofthe material enters between successive beaters so as to be in the path of the striking face of the beaters, successive portions of the material being injected into the successive spaces between the passing beaters. The material is thus `very largely pulverized by impact in its first contact with the beaters,` with resulting improved enlciency of the mill.` Furthermore, there is very little wearing away of the outer edge ,of 'the beaters. Such wear as there is on the striking' face of the beaters does not appreciablyalter A full understanding of the invention canV best be given by a detailed description of a preferred form `of apparatus, and such a description will now be given in connection with the accompany ing drawing showing a. hammer mill of the form now` considered best. `In Asaid drawing:

Fig. 1 is a. sectional view of such a hammer mill in aplane at' right angles `to the axis of the mill rotor; v s i Fig. 2 is a sectional view takenion line 2-'2 of Fig. 1; and

Fig. 3 is e fragmentary Seemann view of e modified construction. v Referring to the drawing. Fig. l shows a hammer mill of known form having cylindrical mill chamber I0 formed by a casing, having an imperforate upper wall Il and a perforate lower wall, or screen, I2 for the discharge' of the pulverized, material. A feed conduit I5 'extends from a feed openingl Ii in one side of the peripheral wall of the chamber, and a high speed rotor i1 is'mounted in the mill chamber, the -rotor 1 having the usual pivotally mounted hammers, or

beaters,l IB. `As indicated by the arrow, and most desirably, therotor is driven in the direction for its beaters to move upward past the feed opening.

The material to be pulverized is fed at a controlled rate from a hopper 20 by meansof one'or V more feed screws 2|, usually, and as shown, three their angularity and, therefore; does not cause f' any appreciable loss in production capacity or in fineness of pulver-ization of the material, and the necessity of more or less frequent renewal or repair of the beaters is avoided. `Also. for some materials, finer screens may be -used for l discharge of the pulverized material from the r mill chamber `with less trouble from clogging such feed lscrews mounted horizontally side by side. The feed screws aredriven in any suitable manner and at a speed to feed the materialfrom the hopper at the desired rate. The material fed from the hopper dropsthrough a chute 22 and through an inlet opening into thefeed conduit I5 directly in advance of a restricted air inlet, or nozzle opening, 23 to which airis supplied through s a conduit or pipe 24 from any suitabley source of air under pressure. The feed conduit l5 extends' most desirably radially of the rotorand mill chamber and is oblong in crosssection,' being particles move substantially 1/2 inch radially of length of the mill chamber, and for a mill having I a very short mill chamber the feed opening need not be of oblong form and the feed conduit need not be oblong in cross-section. The feed chute 22 the rotor in the time interval between the passing of successive beaters. In other words, the material is most desirably injected into the path of the beaters ,at a speed measured in inches per second substantially equal to the inch measurement of the width of the beater faces times the number of beater passings per second. This should have a width corresponding to that of the 1 feed conduit, and the number of feed screws, one or'more, will be determined by the width of the conduit and chute.

The air supply conduit 24 merges into the restricted air inlet, or nozzle opening, 23` so that as the air flows from the pipe to the nozzle'pressure energy of the air is converted into velocity energy with the result thatja high velocity stream of air issues from the nozzle opening into the conduit I and carries along with it through the conduit material dropping'into the conduit from the chute 22. in the-air stream and are discharged in suspension in the air stream from the feed opening I6 at high velocity into the path of the beaters. The material kstruck by each beater as it passes the feed opening is, therefore, spread over the striking face of the beater instead of being struck only by the edge of the beater as in hammer mills in which the material is feed into the mill chamber in the heretofore customary Way. Most desirably, the far walll of the chute extending downward from the discharge opening of the -hopper slopes slightly forward and is curved at its lowerend so that theA material entering the conduit is directed forward in the direction of the air flow, thus lessening the inertia of the particles of material to be overcome by the air stream; and most desirably the curve at the bot- 1 tom of the wall ends at the air nozzle opening 4tangent to the issuing air stream or jet. The

chute is closed at the top by a hinged cover 25 to prevent the suction in through the chute of air which would lower the velocity of the air stream entering the mill chamber. y

The speed at which the material should for best results be injected into the path of Ithe'beaters will depend on the time interval at which suc- .cessive beaters pass the feed opening and the radial Width of the striking faces of the beaters;

and for a given `speed of iniection of the material The particles of material become distributedy speed is ordinarily a Speed'of several hundred inches per second.

FB? a hammer mill such as shown in Fig. 1, having a cylindrical mill chamber of about l2 inches in diameter, and a rotor having, as shown, twelve rows of beaters equally spaced circumferentially and extending close to the peripheral wall of the chamber and driven to revolve at 6000 R. P. M ,the beaters will pass the feed opening I6 at the rate'of 1200 per second, the time interinto the path'of 'the beaters, the vertical width of the nozzle opening and the length and vertical dimension, or depth, of the conduit and the pressure under which `the air or other gas is suppliedA to the pipe 24 will vary according to the capacity of the mill per unit'of length of the mill chamber, that is, according to the amount of material passing through the conduit per unit of time in each unit of transverse, or axial, width of the conduit and of the feed opening I6.

k The material should be injected through theA feed opening and into the path of the beaters at a speed such that the particles move in the time interval between the passing of successive beaters 65. 'Through 60 meshm,

a substantial part of an inch, which will be more or less according to the radial width of the striking' faces of the beaters or such part of the forward facing faces of the beaters .as it is` desired Capacity... H P

`Through 200 mesh val between the passing ofrsuccessive'beaters being 1/1200. of a second.v If the beaters have' striking faces 1A; inch wlderadially, then the'speedl at which the material is fed radially into the'path of the beaters should for best results be theoreticauy o inches per second. ,This speed of injection of the material of 600 inches per second, or approximately that, is obtained with material feeding means such as shown in which the feed inlet I6 measures 61/2 inches axially of the mill chamber and 1 inch circumferentially` thereof, the feed conduit I5 is about 5 inches long andfGl/g inches in hqrizontai width-and 1 inchfin vertical lwidth, the nozzleY opening 23 is 61/2 incli'estlong rial to be pulverizedis fed directlyto the1 feed opening and into thevmill chamber by thecommonlyused screw feed. For example, the following comparative results have beenobtained, A

fed to themill chamber'by air injection according to the invention: y Y l Granulated ca'ne sugar Capacity H. P

Through me. Through mesh 900 mslm'. 7 5.

Dental Through 100 mesh l .l

`11 butterfaf' cocoa For hammer mills of substantially larger size and greater capacitythe feed conduit and feed opening should be of correspondingly greater vertical width, andthe injecting air is most l desirablysupplied in two streams through two vertically spaced noazle openings 23' as shown in Fig. 3. g

The physical character and condition of the material to lbe pulverized is not of particular moment except that it should be in the form of particles not too large to pass freely through the feed or mixing conduit, and that, as stated, the material should be more or less disintegratable i edges of which movel close to the chamber wall in passing the feed opening, means for driving the rotor at high speed in the direction to cause its beaters to move upward past the feed opening, a closed feed conduit extending to the, feed opening andmeans for injecting the material to be pulverized through the .feed conduit and through the feed opening into the path of the beaters suspended in, and moving at approximately the same speed as, a currentfof gas moving `at approximately right angles to the directionof movement of the beaters with a speed of several hundred inches per second..

2. An impact pulverizer, comprising a cylindrical chamber having a feed opening in one side of the peripheral wall thereof and the lower portion of its peripheral wall being perforate `for the discharge of pulverized material, a rotor mounted within said chamber having a plurality of circumferentialiy spaced beaters the outer edges of which move close to the chamber wall in passing the feed opening, means for driving the rotor at high speed in the direction to cause its beaters to move upward pastl the feed opening, a closed feed conduit extending to the. feed opening a gas injector which discharges through the feed conduit and through the feed opening into the path of the beaters ahighvelocity stream of gas moving at'appro'ximately right angles to the direction of movement of the beaters with a speedof several hundred `inches per second, and means for supplying the material to 4he pulverized to the mixing tube of said injector to be carried by the gas stream at high velocity through the feed opening and into the path of `the beaters.

3 3. An impact pulverizer, comprising a cylindrical chamber having a feed opening in the peripheral wall thereof and the lower portion of its peripheral wall being perforate for the discharge of pulverized material, a high speed rotor mounted within said chamber having a plurality of circumferentially spaced beaters the outeredges of which move close to the chamber w-all in passing the feed opening, a closed feed conduit extending to said feed opening at approximately right angles to th'e direction in which the beaters move past the `feed opening, means for discharging a high speed jet of gas into the outer end of said conduit, a material feed inlet opening into said conduit near its outer end, a feed hopper, a closed chute extending from the outlet of said hopper down to said feed inlet opening,

- and a feed screw for feeding material to `be pulverized from said hopper to drop through said chute to the feed inlet opening into said conduit.

4. An impact' pulverizer, comprising a cylindrical chamber having in one side of the peripheral wall thereof a feed opening elongated in the direction parallel to the axis of the chamber, theA lower portion of the peripheral wall-of the chamber being perforate for the discharge of pulverized material, a rotor mounted within said chamber having a plurality of circumferentially spaced beaters the outer edges of which move close to the chamber wall in passing the feed opening, means for drivingthe rotor at high speed in the `direction to cause its` beaters to move upward past the feed opening, a closed feed conduit extending to said feed opening at approximately A right angles to the direction in which the beaters pass the opening, said conduit being oblong in `cross-section to correspond tothe feed opening and having a restricted air inlet slot at its outer end, means for supplying gas under pressure to said inlet slot, an elongated material feed inlet opening into said conduit adjacent the gas inlet slot and between it and the feed opening to the mill chamber, a feed hopper, and a plurality of feed screws located side by side for feeding material to be pulverized from said hopper to drop through the feed inlet opening into said conduit.

5. An impact pulverizer, comprising a cylindrical chamber having a feed opening and the lower portion of its peripheral wall being perfo-` rated for thedischarge of pulverized material,` ra high speed rotor mounted within said `chamber having a plurality of circumferentlallyfspaced` WILLIAM M. srmrnoN. 

